Coating apparatus and system

ABSTRACT

Coating apparatus having a chamber with means mounted in the chamber for carrying a plurality of substrates to be coated. First and second sources are disposed in the chamber and contain coating materials which can be evaporated to produce vapor streams. Masking means is disposed between the first and second sources and the substrates for controlling the amount of each of the coating materials deposited by the vapor stream upon the substrates. The masking means includes a pair of masks and means for moving the pair of masks in accordance with a preprogrammed function so that a coating is deposited on the substrates which is comprised of a mixture of the coating materials having proportions related to the preprogrammed function. The means for moving the pair of masks includes first and second coaxially aligned shafts secured to the masks, a pair of drive motors, gearing connecting the drive motors to said shafts, and means for operating the motors in accordance with said preprogrammed function. The means for operating the motors includes control means for one of the motors comprising a reference following said preprogrammed function, means for sensing the position of the shaft of said one drive motor and means for comparing the reference signal with the position of the shaft to provide an error signal and means for driving said one motor until the error signal is reduced to zero.

States Patent 115] 3,36, 1 6 'lhelen et a1. 45 Ji 25, 1972 1541 CUATINGAPPARATUS AND SYSTEM FOREIGN PATENTS OR APPLICATIONS Inventors; J.Thelen; H. Be -gig; E gene 1,3 France A, E f i n f Santa Rosa, C lif1,051,402 12/1966 Great Britain ....1 18/495 492,464 3/1954 ltaly...'..118/49 [73] Assigneez Optical Coating Laboratory, l1r1c., Santa RosaCallf- Primary ExaminerMorris Kaplan [221 Filed; Mal. 14 1966Attorney-Flehr, Hohbach, Test, Albritton 8L Herbert 1 1 pp 533,996 57ABSTRACT Coating apparatus having a chamber with means mounted in [52]US. C11 ..118/8, 1 18/48 the chamber for carrying a plurality ofsubstrates to be coated. l- B050 1 U First and second sources aredisposed :in the chamber and con- [58] Field of Search ..1l8/1-11,48-49.5, tain coating materials which can be evaporated toproduce 219/271, 27 vapor streams. Masking means is disposed between thefirst 117/106-107.2 and second sources and the substrates forcontrolling the amount of each of the coating materials deposited by the[56] References Cited vapor stream upon the substrates. The maskingmeans in cludes a pair of masks and means for moving the pair of masksUNITED STATES PATENTS in accordance with a preprogrammed function sothat a coat- 2,160,981 6/1939 OBrien ..118/49 x 8 is deposited on theSubstrates which is eemprieed efe 2,239,642 4/1941 Burkhardt et a1...118/49 UX ture of the coating materials having proportions related tothe 2,432,950 12/1947 Turner et 31"" "118/49 preprogrammed function. Themeans for moving the pair of 2,771,055 1 H1956 Kelley et a1. ..1 18/9masks includes first and second coaxially aligned shafts 2,860,07511/1958 Alexander et a1 ..118/49.1 x Secured to masks e Peh hive metersgearing Connect 2,906,235 9/1959 Hirsh ..118 9 x leg the drive meters toSaid Shafts, and means for Operating 3,023,727 3/1962 Theodoseau et a1...1 18/49 X the motors in accordance with said preprogrammed function.3,157,535 11/1964 Radke ..118/7 The means for Operating the metersincludes eehhel means 3,211,128 10/1965 Potter et al. 118/49 1 for oneof the motors comprising a reference following said 3,238,918 3/1966Radke et a1 118/49 1 preprogrammed function, means for sensing theposition of 3,312,190 4/1967 Bradshaw 1 153/49 he shaft of said onedrive motor and means for comparing the 3,316,386 4/1967 Yaffe et al.18/49 X reference signal with the position of the shaft to provide an3,336,154 8/1967 Oberg 6 3L t 118/491 X error signal and means fordriving said one motor until the 3,347,701 10/1967 Yamagishi et 3.1..1l8/49.1 x error Signal redheed Zere- 3,378,676 4/1968 Clement .1...118/9 X 3,397,672 8/1968 Dykeman et a1 ..118/49.5 5 7 Draw F'gms v asOZ 1 1p aim mwss'i 41:71 11:1" Illllifl- {aural/III)? N1"A\\\\\\\\\\\PATENTED JANZSIBYZ 338301 sum 1 or 5 (D e m 'w? v O O O O m s,

m VENTORS Alfred J. The/en Attorneys PATENTED mm 3,636,916

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FNVENTORS Alfred J. The/en Nils H Bergfelr Eugene A. Eufusia AttorneysPATENTED JAHZS I972 SHEET h 0F 5 INVENTORS Alfred J. Thelen Nils H. Berfelt Eugene A. gufusia 6% @249 Attorneys PATENTED JAMES I972 ,6 3 m l ESHEU [1F 5 203 9: 202 SCHMITT 207 208 MM STEPPWG ,3! I TRIGGER MoTom 2uruuww A8 I SHAFT mFFER 11;: i'LP MOWER 20 L- POS. W FLOP POT.

\ STABLE 2II T Cum/E VARIMLE f w f VOLTAGE TRACER REF VOLTAGE SUPPLY 212SUPPLY DESIRED sMmF'r POEMTEOIM mom LINEAR AMP. 219 22/ 222 223 W DOUMLEDIFE COMPENSATOW coMPEmsm'ow ggwgg MR R0, +1) W, (SRyCsi-IZ (smog +1) 1%(5W, a, +1)

MANUALLY CONTROLLED 229, VARIMC 228 226 (2 @om' w MOTOR STEW TRANS.DRIVEN oowm K ST vmmc TRANS.

I We 4) 227 ST: K;

I'NVENTORS comma srranmms AND svsrmvr This invention relates to acoating apparatus and system.

In coating operations, it often is desirable to utilize two coatingmaterials and to deposit them simultaneously in a predeterminedrelationship. With existing coating machines, this is very difficult todo. In addition, it is very difficult to monitor the rate of depositionof each type of material. There is, therefore, a need for a new andimproved coating apparatus, system and method, and a rate monitor foruse therein.

In general, it is an object of the present invention to provide acoating apparatus and system in which one or more evaporation sourcesmay be utilized independently of each other or at the same time.

Another object of the invention is to provide an apparatus and system ofthe above character in which the evaporation rate from any source can becontrolled automatically.

Another object of the invention is to provide an apparatus and system ofthe above character in which the rate of evaporation from the coatingsources can be made to follow a preprogrammed function.

Another object of the invention is to provide an apparatus and system ofthe above character in which the proportions of the different coatingmaterials can be readily controlled.

Another object of the invention is to provide an apparatus and system ofthe above character in which the proportioning of the coating materialsis automatically programmed.

Another object of the invention is to provide an apparatus and system ofthe above character in which the rates of deposition of the materialscan be monitored optically.

Another object of the invention is to provide an apparatus and system ofthe above character which does not require the use of separate chips.

Another object of the invention is to provide an apparatus and system ofthe above character which is particularly useful for controllingdeposition where a constant rate of deposition is required.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodi ment is set forth indetail in conjunction with the accompanying drawings.

Referring to the drawings:

FIG. 1 is a cross-sectional view of a coating apparatus incorporatingthe present invention.

FIG. 2 is an enlarged cross-sectional view of the mask indexingassembly.

FIG. 3 is a view looking along the line 3-3 of FIG. 2 and showing themasks of the mask-indexing assembly.

FIG. 4 is an enlarged cross-sectional view of the rate monitor.

FIG. 5 is a view looking along the line 5-5 of FIG. 4 and shows thecover plate with the aperture therein and the mask for adjusting thesize of the aperture.

F116. 6 is a block diagram of the electrical circuitry for themask-indexing assembly.

FIG. 7 is a block diagram of the electrical circuitry for the automaticrate-control system.

In general, the coating apparatus and system includes a chamber withmeans mounted in the chamber for carrying a plurality of substrates tobe coated. First and second sources for vapor streams are disposedwithin the chamber. A particularly unique means is provided formonitoring the rate of evaporation from the sources. In addition, meansis connected to the monitoring means and to the sources for causing theevaporation rate from the vapor sources to follow a preprogrammedfunction. In addition, masking means is provided for controlling theflow of vapor from each of the sources to the substrates being coated.Means is provided for automatically controlling the masking assembly tocause the deposition of the coating materials upon the substrate in apredetermined relationship.

As shown in the drawings, the coating apparatus incor porated in thepresent invention consists of an enclosed vacuum chamber or housing 11which includes a sidewall 12, a bottom wall 13 and atop wall 14. First.and second source assemblies 16 and 17 are mounted in the bottom walland are adapted to supply vapor streams to the substrates 13 to becoatedcarried by a rotatable rack assembly 19. A mask-indexing assembly21 is mounted in the bottom wall between the first and second sourceassemblies 16 and 17. Means is provided for monitoring the rate ofdeposition of vapors upon the substrate 18 and consists of first andsecond substrate-shifting assemblies 22 and 23 and first and secondoptical monitors 26 and 27. The optical monitors are of a type disclosedin copending application Ser. No. 321,888, filed Nov. 6, 1963, now US.Pat. No. 3,41 1,852 and as disclosed therein, each includes a sensingassembly 28.

The first and second source assemblies 16 and 17 are substantiallyconventional and each consists of a pair of conducting rods 29 and 31carried by mounting plate 32 formed of insulating material secured tothe bottom wall 13. The rods 29 and 31 extend through an opening 33provided in the bottom wall 13. The rods 29 and 31 carry a supportassembly 34 which mounts a boat 36. As is well known to those skilled inthe art, the support assembly 34 is arranged so that when power issupplied to the rods 29 and 31, power flows through the boat 36 which isformed of a resistive-type material to heat the source material carriedtherein to cause the same to vaporize within the chamber 11. Power issupplied to the source assemblies 116 and 17 by transformers 37 whichare connected to a suitable source of power (not shown).

As explained previously, the vapors from the boats 36 are adapted toimpinge upon the substrates 18 carried by the rack assembly 19. The rackassembly 19 consists of a rack 41 of conventional construction which ismounted upon a spindle 42 rotatably carried by ball-bearing assemblies43 mounted in a bearing housing 44. The spindle 42 is also held in placeby a plate 46 which is secured to the lower extremity of the bearinghousing 44 by screws 47. The bearing housing 44 extends upwardly throughan opening 48 provided in the top wall 14 and is secured to a mountingplate 49 which is secured to the top wall 14 by cap screws 51. A shaft52 is rotatably mounted in the mounting plate 49 and is connected to thespindle 42 by a pin 53. The shaft 52 is rotated by suitable motive meanssuch as an electric motor and a speed reducer (not shown) to rotate therack 41 at a predetermined rate.

Mask-Indexing Assembly 21 The flow of vapors to the substrates 13carried by the rack 41 is also controlled by the mask-indexing assembly21. The mask-indexing assembly 21 is shown in detail in FIG. 2 andconsists of a large housing 61 which is secured to a mounting plate 62by screws 63. The mounting plate 62 overlies an opening 64 provided inthe bottom wall 13. Suitable means is provided for forming a sealbetween the plate 62, the bottom wall 13 and the housing 61 and consistsof O-rings 66 and 67.

The mask-indexing assembly 21 also includes first and second masks 71and 72 which are carried by concentric shafts 73 and 74. The mask 71 isa 180 mask as hereinafter described and is secured to the shaft 73 by asplit hub 76. The mask 72 consists of two masks and is mounted upon asplit hub 77 which is mounted upon an enlarged end member '73 secured tothe upper extremity of the shaft 74 by suitable means such as welding.The shaft 74 is: rotatably mounted in ball-bearing assemblies 79 carriedin a bearing housing 61. The bearing housing 31 is provided with aflange 82 which is secured to the housing 61 by screws 33. The bearingassembly 79 is held in place by retaining rings 114. The bearing housing61 is provided with openings 66 and the shaft 74 is provided withopenings 87 which communicate with the interior of the chamber 111. Theinner concentric shaft 73 is rotatably mounted within the outer shaft 74by a ball-bearing assembly 63 which is held in place by a retaining ring39.

Means is provided for driving the shafts 73 and 74 and consists of gearmotors 91 and 92. The gear motors 91 and 92 can be of any suitable typeas, for example, the gear motor 91 can have a range of output speedsfrom to 100 r.p.m., whereas the gear motor 92 can have a range of outputspeeds from 0 to 60 r.p.m. The 'gear motors 91 and 92 are mounted upon aplate 93 which is secured .to the housing 61 by screws 94. A suitableseal is provided in the form of an O-ring 96.

The gear motor 92 is provided with an output shaft 97 which is connectedto a coupling 98 by the tongue-and-slot connection shown. The coupling98 is connected to the center shaft 73 by a pin 99. The coupling 98 isrotatably mounted in bearing assemblies 101 which are held in place byretaining rings 102. The bearing assemblies 101 are mounted in acylindrical extension 61a formed as an integral part of the housing 61.A sun gear 103 is mounted upon the coupling 98 and drives a planetarycluster gear 104 mounted upon a hub 106. The hub 106 is secured to ashaft 107 by a pin 108. The shaft 107 is rotatably mounted in a pair ofball-bearingassemblies 109 which are carried by a planetary arm 111 andretained therein by rings 112. The planetary arm 111 is mounted upon alarge hub 113 which is rotatably mounted by ball-bearing assemblies 1 14on the outer surface of the cylindrical extension 61a and which areretained thereon by retaining rings 1 16. A large planetary gear 117 ismounted on the large hub 113 and is driven by the small gear 118connected to the output shaft 119 of the gear motor 92 by pin 121.Another gear 123 is mounted on the hub 106 and drives a large gear 124mounted upon a hub 126 secured to the lower extremity of the outer shaft74 by set screw 127.

In addition, the gear motor 91 is directly connected to a motor-drivenpotentiometer 131 which gives an exact indication of the shaft positionof the gear motor 91.

Monitor Substrate-Shifting Assemblies 22 and 23 The monitorsubstrate-shifting assembly 23 is shown in detail in FIG. 4 of thedrawings. As shown therein, it consists of a substrate 141 formed of asuitable material such as a glass or quartz disc and having a suitablediameter such as 8 inches. The substrate 141 is carried by a hubassembly 142 mounted upon a shaft 143. The shaft 143 is rotatablymounted in a bearing housing 144 by a pair of ball-bearing assemblies146. The housing 144 is mounted upon the top wall 14 of the chamber 11and secured thereto by suitable means such as capscrews 147.

The hub assembly 142 consists of an upper hub member 148 which isslidably mounted on the lower extremity of the shaft and is normallyretained thereon by a retaining ring 149 mounted on the shaft 143. Aspring 151 is disposed on the shaft 143 and has its lower extremityengaging the upper portion of the upper hub member 148 and has its upperextremity engaging a retaining ring 152 secured to the shaft 143. Thehub assembly 142 also includes a lower hub member 154 which is securedto the lower end of the shaft 143 by a pin 156. The lower hub member 154engages the lower surface of the substrate 141 and is provided with apin 157 which is disposed in a hole 158 provided in the substrate 141 sothat when the shaft 143 is rotated, the substrate 141 is driven thereby.In addition, the spring 151 yieldably urges the upper hub member 148into engagement with the upper surface of the substrate 141 so that thesubstrate 141 is firmly clamped between the upper hub member and thelower hub member 154.

The shaft 143 is driven by a speed reducer 161 which is mounted in aspeed-reducer housing 162. The housing 162 is mounted upon the bearinghousing 144 by a plate 163 which is secured to the bearing housing 144by screws 164 and to the speed-reducer housing 162 by screws 166. Thespeed reducer 161 is provided with an output shaft 167 which is disposedin a bore 168 provided in the shaft 143 and is pinned to the shaft 143by a pin 169. The speed reducer 161 is driven by an electric gear motor171 which is secured to the speed-reducer housing 162 by screws 172. Themotor is provided with an output shaft 173 which is connected by acoupling 174 to an input shaft 176 of the speed reducer 161. The gearmotor 171 can be of any suitable type as, for example, it can be onewhich has an output shaft which rotates at a speed of 60 r.p.m. Thespeed reducer 161 can still further reduce the speed so that the speedof rotation of the output shaft 167 is approximately o'ne-halfrevolution per hour.

Means is provided so that only a predetermined portion of the substrate141 is exposed at any one time and consists of a main circular coverplate 181 secured to an annular bracket 182 by bolts 183; the bracket182 is secured to the bottom surfaces of the top wall 14 of the chamber1 1 by screws 184. The cover plate 181 is provided with an arcuateopening or aperture 186 which subtends a suitable angle as, for example,an angle of The opening 186 is also of a suitable width as, for example,1 inch. As can be seen from FIG. 4, the opening 186 is defined on oneside by an inclined surface 187 provided in the cover plate 181 which isinclined in the direction in which the vapors pass from the coatingsources 16 and 17. A centrally disposed mounting member 188 is mountedupon the cover plate 181 and carries means which makes it possible toclose off any portion or all of the opening 186. Such means consists ofa segment or mask 191 which preferably subtends an angle which isgreater than the angle subtended by the opening 186 so that the openingor aperture can be closed. The segment 191 is mounted upon a hub 192.The hub 192 is secured by suitable means such as a screw 193 and washer194 to the mounting member 188. It can be seen that merely by looseningthe screw 193, the segment or mask 191 can be shifted to any desiredangular position to close off any desired portion of the opening oraperture 186.

A plate 196 is secured to the cover plate 181 by suitable means such aswelding and depends therefrom in a vertical direction. As can be seenfrom FIG. 4, it is mounted on the cover plate 181 between the opening186 and the source which is farthest away so that the substrate 141 willonly receive vapors from the closest source and not from the othersource, as illustrated in FIG. 1.

Electrical Circuitry Suitable electrical circuitry is provided as a partof the coating apparatus and includes electronics shown in block diagramform in FIG. 6 for the mask-indexing assembly and electronics shown inblock diagram form in FIG. 7 for the automatic rate control system. Theelectronics which is shown in FIG. 6 forms a part of the coatingapparatus and is provided to form a system which automatically programsthe mixture proportion of two coating materials from the sources 16 and17 by controlling the mask-indexing assembly 21.

Electronics of the type shown in FIG. 6 is provided for the steppingmotor 91 of the mask-indexing assembly 21. As shown in FIG. 6, theelectronics includes a curve tracer 201 of a suitable type such asmanufactured by the F. L. Moseley Division of Hewlett-Packard Company.As is well known to those skilled in the art, the curve tracer isadapted to receive a sheet of paper upon which there is deposited aconducting ink which represents the proportionality relationship for thecoating which is to be deposited upon the substrates 18 carried by therack assembly 19. The curve tracer 201 produces a signal proportional tothe shape of the curve and supplies it to a differential amplifier 202.The signal from the curve tracer 201 serves as a reference signal andthis signal is compared with a signal coming from the shaft positionpotentiometer 131 assuming that it is the stepping motor 91 which isbeing controlled by the electronics shown in FIG. 6. The differentialamplifier takes the difference between the reference signal and thesignal from the shaft position potentiometer 131 and supplies what iscalled an error output signal into two Schmitt trigger circuits 203 and204. If the error is a positive error, the Schmitt trigger circuit 203is operated, whereas if the error is negative, the other Schmitt triggercircuit 204 is operated. If the error is negative; or, in other words,on one side of zero or of one polarity, a relay 204 is operated by thetrigger circuit 204 which is connected to the motor @l to reverse thedirection of rotation of the stepping motor 931.

lf either a negative or a positive error signal is supplied by thedifferential amplifier to the Schrnitt trigger circuits 2% and 2%, abistable flip-flop 2b? is triggered. The bistable flipflop 2th? is of atype which supplies a square wave to a power amplifier illlll. Thebistable flip-flop 207 is also a type which, once triggered, will lreerun until the error signal is zero. The stepping motor ill is of asuitable type such as SLU-SYN 400 which is stepped by the square wavefrom the power amplifier 2llll. Stepping of the motor 9i causes the maskll carried thereby to be shifted and at the same time causes thepotentiometer lill to be rotated a proportional amount until a signal isfed back to the differential amplifier 202 to reduce the error signalfrom the amplifier 202 to zero. As soon as there is no error, theSchrnirt trigger circuits ass and d are triggered to turn oh" thebistable flip-flop 2'07 which stops freerunning and which, in turn,causes the stepping motor ill to stop rotating. As can be seen from FlG.t5, stable voltage supplies 2llll and 2ll2 are provided for the curvetracer 2m and for the potentiometer lldll, respectively.

Motor 92 is a nonprogrammed constant speed motor which operates directlyon 1 l5 vac-line voltage.

By utilizing this type of automatic control, it can be seen I that theindex of refraction of the material being deposited on the substrate canbe varied from the index of refraction of one material being evaporatedin the chamber ill to the index of refraction of the other materialbeing evaporated in the chamber ll. in addition, it is possible to makea smooth transition between the indices of refraction of the twomaterials being utilized.

The automatic rate control system which is shown in lFlG. '7 is providedfor controlling the rate of evaporation from each of the first andsecond source assemblies 116 and 17. in the coating apparatus hereindescribed, the automatic ratecontrol system is utilized for maintaininga constant rate of evaporation from each of the coating sources lb and1'). However, it should be appreciated that this automatic rate controlsystem can be utilized for providing a rate of evaporation following anypreprogrammcd function. When a constant coating rate is desired, aconstant reference is supplied to the reference terminal 2117 in HQ. '7.If a preprogrammed function is to be followed, the function may beapplied to a chart mounted on a curve tracer. The output from the curvetracer is supplied to the reference terminal 2ll'7. The rate ofevaporation from the boat 36 is monitored by the evaporation ratemonitor 27 and its transducer 2% which supplies a signal to an amplifier21in. The amplifier Zlh can be of any suitable type such as the Type415D manufactured by Hewlett-Packard Company.

The output from the amplifier 2w is supplied to a differential amplifierare which compares this feedback signal with the reference signalsupplied to the differential amplifier from the reference terminal 2T7.The error signal which is supplied by the differential amplifier ismeasured by the error meter Ml. The error signal is fed into a firstcompensator 22l through a nonlinear amplifier 22b and then to a secondcompensator The compensators 222i and 222 prevent the system fromhunting beyond desired ranges or, in other words, to prevent the systemfrom becoming unstable. The first compensator generates a phase leadwhich is utilized for compensating for the dead time in the evaporationrate monitor. This dead time occurs because it takes a predeterminedamount of time for the monitor disc ll ll to rotate past the window oropening lhti provided in the main cover lhll. The amount of this deadtime changes as the window size is changed. The second compensator 222generates a phase lead with a phase lag and compensates for a long timedelay constant which is caused by the time required to change thetemperature of the boat to change the evaporation rate.

The output from the second compensator 222 is supplied to to a doubleSchmitt trigger and relay 2235, similar to that shown in FIG. h, whichserves as a relay with dead time. The

double Schmitt trigger and relay 223 supplies an output to amotor-driven Variac 22h which supplies: either a bucking or a boostingvoltage to the primary of a stepdown transformer 22?. The stepdowntransformer 227, in turn, supplies a bucking or boosting voltage to aboat transformer 22b in series with the voltage supplied by a manuallycontrolled Variac 229. The boat transformer 22% then supplies a voltageto the boat 36 to heat the boat. lleating the boat causes material inthe boat to evaporate to cause a vapor stream to flow therefrom and tobe deposited upon the monitor substrate Mill. The rate the material isdeposited upon the substrate ldl is monitored by the evaporation ratemonitor 27 which supplies a signal to the amplifier 2m to provide thefeedback signal for the differential amplifier 2119 as hereinbeforedescribed. When the error signal from the differential amplifier 2119reaches zero, the double Schmitt trigger circuit 223 will be turned offto stop the motor driven Variac 22s.

it will be noted that a number of blocks shown in FIG. 7 have beenprovided with conventional feedback control notation to indicate themanner in which they are designed.

Operation of the coating apparatus and system is performing this methodcan now be described briefly in conjunction with the rate monitor. Letit be assumed that the rack assembly 119 has been loaded with substrateslid to be coated and that the desired materials to be utilized for thecoating operation have been placed in the boats 36. The coatingapparatus can then be placed in operation. The rack assembly l9 iscontinuously rotated and the mask-indexing assembly 21 is placed inoperation. Then, either one or both the source assemblies lb and 17 arealso placed in operation to heat the boats as. It should be appreciated,however, that the mask-indexing as sembly 21! is under the control ofelectronics of the type shown in FIG. 6, whereas the source assemblieslb and l7 are under the control of electronics such as that shown inFIG. 7.

As can be seen from FIG. l, while the coating apparatus is in operation,the masks 711 and 72 are positioned so that they control the flow of thevapor stream from each of the sources 356 to the substrates 13 carriedby the rack assembly l9. Also, it can be seen from FlG. l that each ofthe monitor substrate shifting assemblies will only receive a vaporstream from one of the two sources contained in the coating apparatus.This is because the member 1196 prevents the vapor stream from the otherof the sources from reaching the opening or window lllili provided inthe cover plate llbll. it also should be noted that the monitorsubstrate-shifting assemblies 22 and 23 actually see the vapor streamfrom their respective sources without their being chopped by the masks7i and '72. In other words, they see their respective vapor sourcescontinuously. By controlling the source assemblies in and T7 so theysupply vapors at a constant rate to the monitor substrate-shiftingassemblies, it can be seen that by changing the phase relationship ofthe masks 7i and '72 under the control of the electronics shown in H6.ti, it is possible to vary the rate of deposition of each of the coatingmaterials upon the substrates lb. With the arrangement shown, it can beseen that coatings of the two different types of material can bedeposited upon the substrates separately, or they can be depositedsimultaneously to obtain any desired mixture. Thus, one layer upon thesubstrate can consist of 30 percent of one coating material, and 70percent of the other coating material. Also, with the coating apparatusshown, it is possible to make a continuous transition from one index ofrefraction for one coating material to other index of refraction for theother coating material. Also, it is possible to utilize the apparatusfor providing a layer which has an index of refraction which is betweenthe ones available from the two materials being utilized. Thus, it ispossible by evaporating both materials simultaneously to obtain a layerhaving an index of refraction which has the same ratio as the mixture ofthe coating materials. For example, a layer comprised of 50 percent ofone material and 50 percent of the other material should be given anindex of refraction which is between the indices of refraction of thetwo materials. in this way, it is possible to make coatings havingindices of refraction which are not available from materials whichappear in nature.

During the entire coating operation, the monitor substrates 141 arerotating very slowly. For example, in one embodiment of the invention,the glass disc rotated has a speed of approximately one-half revolutionper hour. With this speed of rotation, it was found that each point ofthe substrate 141 was exposed to the vapor stream for 3% minutes. Bymeasuring the rate of deposition at the end of the opening 186, it ispossible to measure the average rate with the Bis-minute time constant.This evaporation rate is being monitored by the evaporation rate monitor27. If the evaporation rate changes, the thickness of the layer on thesubstrate 141 changes which, in turn, changes the reflectance which ismeasured by the monitor 27 to give a direct indication of the rate ofevaporation of the coating vapors.

The size of the opening 186 determines the thickness of the layer whichis measured by the monitor 27. There are a number of conflictingconsiderations involved. On the one hand, it is desirable to measure thereflectivity as quickly as possible in order to obtain a system whichhas a fast reaction. On the other hand, it is desirable to wait a periodof time to make the measurements so that the coating will have athickness which will give a large reflectivity which can be easily andaccurately measured. The size of the opening of the hole 186 is,therefore, chosen so that it is a comprise between these two conflictingconsiderations. Thus, for a disc having a diameter of approximately 8inches, an opening of 541 inch has been found to be satisfactory.

In addition, the opening 186 should be positioned so that it can see thesource of the coating vapors at all times and will not at any time beobstructed by the masks 71 and 72. In view of the fact that adhesionneed not be considered, the angle of incidence of the vapor stream onthe substrate 141 is not particularly critical.

The substrate 141 is rotated at a relatively slow speed so that in onerevolution of the same, one complete coating comprised of many layerscan be completed. It can be readily appreciated that if longer coatingperiods are required, larger glass discs can be provided for thesubstrates 141 to give the additional required time. Alternatively, thedisc or substrate 141 can be rotated at a still slower rate.

The optical rate monitoring system utilized in the coating apparatus hasmany advantages. It is relatively stable and gives a larger signal thanconventional devices. In addition, it is very rugged and reliable. Therate monitor herein disclosed may be useful in other applications. Forexample, it may be useful for a continuous process in which it isdesired to deposit a coating of uniform thickness throughout theprocess.

It is apparent from the foregoing that we have provided a coatingapparatus, system and method, and rate monitor therefor in which one ormore evaporation sources may be utilized independently of each other orat the same time. The rate of evaporation from any of the sources can becontrolled automatically and can be made to follow a preprogrammedfunction. In addition, the rates of deposition of the materials upon thesubstrates to be coated can be readily controlled by the use of themasking assembly. At the same time, the rate of evaporation can bereadily monitored to give the desired control.

We claim:

1. In a coating apparatus, a chamber, means mounted in the chamber forcarrying a plurality of substrates to be coated, first and secondsources disposed in the chamber and containing coating materials whichevaporate to produce vapor streams which impinge upon the substrates todeposit the coating material thereon, means for monitoring the rates ofevaporation of the materials from said sources, means connected to themonitoring means and to the first and second sources for causing theevaporation rates of the materials from the first and second sources tofollow predetermined functions, and masking means for controlling theamount of each of the coating materials deposited by the vapor streamsupon the substrates, said masking means including a pair of coaxialshafts rotatably mounted in the chamber first and second masks securedto said coaxial shafts, one of said masks being rotatable with each ofthe coaxial shafts, a pair of drive motors, a planetary gearing assemblyconnecting said drive motors to said first and second coaxial shafts andmeans for causing said motors to operate in accordance with apreprogrammed function.

2. In a system for coating substrates, a chamber, means mounted in thechamber for carrying a plurality of substrates to be coated, first andsecond sources disposed in the chamber and containing coating materialswhich can be evaporated to produce vapor streams which impinge upon thesubstrates, means for monitoring the rates of evaporation of thematerials from said sources, electrical circuitry connected to themonitoring means and to said first and second sources for causing theevaporation rates of the materials in said first and second sources tofollow predetermined functions, masking means disposed within thechamber and adapted to be moved into position to interfere with thevapor streams travelling to the substrates, and means for causing saidmasking means to move in accordance with a preprogrammed function sothat a layer is deposited on the substrates which has an index ofrefraction which is proportional to the relationship in which the vaporstreams from the first and second sources are impeded by the maskingmeans, said electrical circuitry connected to said monitoring means andto said first and second sources including a reference representing thepredetermined function, means for receiving the signal from themonitoring means representing the evaporation rate from one of thesources, and means for comparing the signal from the monitoring meanswith the reference to produce an error signal, means for makingcompensations in the error signal due to dead time, first and secondtrigger circuits, means for supplying the compensated error signal tothe first and second trigger circuits, one of said trigger circuitsbeing triggered when the error signal is of one polarity and the otherof said trigger circuits being trig gored when the error signal is ofthe opposite polarity, a transformer connected to said one source,motor-driven means connected to the trigger circuits and to thetransformer for varying the voltage applied to the transformer inaccordance with the output of the trigger circuits, and means connectedto the trigger circuits for reversing the direction of the motordrivenmeans when the error signal is of one polarity.

3. A system as in claim 2 wherein said means for causing said maskingmeans to move in accordance with the preprogrammed function includesfirst'and second masks, first and second motors for driving said masks,means for sensing the shaft position of each motor, a reference for eachof said motors following said preprogrammed function, means forcomparing the reference with the signal representing the shaft positionof the motor and supplying an error signal, first and second triggercircuit means connected to said comparing means and receiving the errorsignal, one of said trigger circuits being triggered when the errorsignal is of one polarity and the other of the trigger circuits beingtriggered when the error signal is of the opposite polarity, meansconnected to the first and second trigger circuits for driving one ofsaid motors to a position in which the error signal is zero and meansconnected to one of the trigger circuits for reversing the direction ofrotation of the motor when said one trigger circuit is triggered.

4. In a coating apparatus, a chamber, means mounted in the chamber forcarrying a plurality of substrates to be coated, first and secondsources disposed in the chamber and containing coating materials whichcan be evaporated to produce vapor streams, and masking means disposedbetween said first and second sources and said substrates forcontrolling the amount of each of the coating materials deposited by thevapor streams upon the substrates, said masking means including a pairof masks and means for moving said pair of masks in accordance with apreprogrammed function so that a coating is deposited on the substrateswhich is comprised of a mixture of the coating materials havingproportions related to said preprogrammed function, said means formoving said pair of masks including first and second coaxially alignedshafts error signal is reduced to zero.

5. Apparatus as in claim 4 wherein said means for driving the motorincludes a pair of trigger circuits, a bistable flip-flop connected tothe output of one of the trigger circuits, means connected to the outputof the flip-flop for driving the motor, and means connected to thetrigger circuits for reversing the direction of advance of the motorwhen the error signal assumes a value of one polarity.

1. In a coating apparatus, a chamber, means mounted in the chamber forcarrying a plurality of substrates to be coated, first and secondsources disposed in the chamber and containing coating materials whichevaporate to produce vapor streams which impinge upon the substrates todeposit the coating material thereon, means for monitoring the rates ofevaporation of the materials from said sources, means connected to themonitoring means and to the first and second sources for causing theevaporation rates of the materials from the first and second sources tofollow predetermined functIons, and masking means for controlling theamount of each of the coating materials deposited by the vapor streamsupon the substrates, said masking means including a pair of coaxialshafts rotatably mounted in the chamber first and second masks securedto said coaxial shafts, one of said masks being rotatable with each ofthe coaxial shafts, a pair of drive motors, a planetary gearing assemblyconnecting said drive motors to said first and second coaxial shafts andmeans for causing said motors to operate in accordance with apreprogrammed function.
 2. In a system for coating substrates, achamber, means mounted in the chamber for carrying a plurality ofsubstrates to be coated, first and second sources disposed in thechamber and containing coating materials which can be evaporated toproduce vapor streams which impinge upon the substrates, means formonitoring the rates of evaporation of the materials from said sources,electrical circuitry connected to the monitoring means and to said firstand second sources for causing the evaporation rates of the materials insaid first and second sources to follow predetermined functions, maskingmeans disposed within the chamber and adapted to be moved into positionto interfere with the vapor streams travelling to the substrates, andmeans for causing said masking means to move in accordance with apreprogrammed function so that a layer is deposited on the substrateswhich has an index of refraction which is proportional to therelationship in which the vapor streams from the first and secondsources are impeded by the masking means, said electrical circuitryconnected to said monitoring means and to said first and second sourcesincluding a reference representing the predetermined function, means forreceiving the signal from the monitoring means representing theevaporation rate from one of the sources, and means for comparing thesignal from the monitoring means with the reference to produce an errorsignal, means for making compensations in the error signal due to deadtime, first and second trigger circuits, means for supplying thecompensated error signal to the first and second trigger circuits, oneof said trigger circuits being triggered when the error signal is of onepolarity and the other of said trigger circuits being triggered when theerror signal is of the opposite polarity, a transformer connected tosaid one source, motor-driven means connected to the trigger circuitsand to the transformer for varying the voltage applied to thetransformer in accordance with the output of the trigger circuits, andmeans connected to the trigger circuits for reversing the direction ofthe motor-driven means when the error signal is of one polarity.
 3. Asystem as in claim 2 wherein said means for causing said masking meansto move in accordance with the preprogrammed function includes first andsecond masks, first and second motors for driving said masks, means forsensing the shaft position of each motor, a reference for each of saidmotors following said preprogrammed function, means for comparing thereference with the signal representing the shaft position of the motorand supplying an error signal, first and second trigger circuit meansconnected to said comparing means and receiving the error signal, one ofsaid trigger circuits being triggered when the error signal is of onepolarity and the other of the trigger circuits being triggered when theerror signal is of the opposite polarity, means connected to the firstand second trigger circuits for driving one of said motors to a positionin which the error signal is zero and means connected to one of thetrigger circuits for reversing the direction of rotation of the motorwhen said one trigger circuit is triggered.
 4. In a coating apparatus, achamber, means mounted in the chamber for carrying a plurality ofsubstrates to be coated, first and second sources disposed in thechamber and containing coating materials which can be evaporated toproduce vapor streams, anD masking means disposed between said first andsecond sources and said substrates for controlling the amount of each ofthe coating materials deposited by the vapor streams upon thesubstrates, said masking means including a pair of masks and means formoving said pair of masks in accordance with a preprogrammed function sothat a coating is deposited on the substrates which is comprised of amixture of the coating materials having proportions related to saidpreprogrammed function, said means for moving said pair of masksincluding first and second coaxially aligned shafts secured to saidmasks, a pair of drive motors, gearing connecting said drive motors tosaid shafts, means for operating said drive motors in accordance withsaid preprogrammed function, said means for operating said motorsincluding control means for one of the motors comprising a referencefollowing said preprogrammed function, means for sensing the position ofthe shaft of said one drive motor and means for comparing the referencesignal with the position of the shaft to provide an error signal, andmeans for driving said one motor until the error signal is reduced tozero.
 5. Apparatus as in claim 4 wherein said means for driving themotor includes a pair of trigger circuits, a bistable flip-flopconnected to the output of one of the trigger circuits, means connectedto the output of the flip-flop for driving the motor, and meansconnected to the trigger circuits for reversing the direction of advanceof the motor when the error signal assumes a value of one polarity.